The environmental requirements for adventitious root initiation and growth in 22-day-old blue grama (Bouteloua gracilis) seedlings were determined under controlled temperature and soil moisture conditions. The seminal root was maintained in moist soil; but surface soil (in which adventitious roots may develop) was independently maintained at various degrees of drought. Drought treatments were imposed by controlling the relative humidity of air above the soil and around seedling crowns. In the 100% humidity treatment, elongation rates of the longest root per seedling at temperatures of 15, 20, 25, and 30 C were 0.40, 0.74, 1.04, and 1.22 cm per day, respectively. In the 96% humidity treatment, elongation rates at these temperatures were 0.28, 0.36, 0.38, and 0.44 cm per day, respectively. When the seminal root is growing in moist soil, blue grama seedlings can initiate adventitious roots during severe drought conditions in the surface soil. However, adventitious root growth adequate for seedling establishment will probably not occur at moisture and temperature conditions of less than 96% humidity (-50 bars) and 15 C.